SPF 100+ sunscreen is more protective against sunburn than SPF 50+, according to a randomized, double-blind, split-face, natural sunlight exposure clinical trial published in the Journal of the American Academy of Dermatology (May 2018). Joshua D. Williams, PhD, et al, performed the study of 199 healthy men and women (≥18 years) in Vail, Colorado. Each participant wore both the SPF 50+ and SPF 100+ (split face) sunscreens simultaneously during activities. They had no restrictions on use and application other than designation of the treatment area. Blinded evaluators assessed erythema on the day following exposure.
Participants averaged 6.1 ± 1.3 hours of sun exposure. The following day, the evaluators identified 55.3 percent of the participants (110 of 199) as more sunburned on the SPF 50+ protected side compared to 5 percent (10 of 199) on the SPF 100+ protected side. In addition, 40.7 percent of subjects (81 of 199) had increased erythema scores on the SPF 50+ protected side versus 13.6 percent (27 of 199) on the SPF 100+ protected side.
Image Creative Commons/By Phil Kates